1. Technical Field of the Invention
The present invention relates to a wiper blade rubber for use in vehicles and the like and also relates to a coating agent coated on this wiper blade rubber.
2. Description of the Related Art
The wiper blade rubber is subjected to a surface treatment with chlorine so as to reduce the frictional resistance in wiping and improve the abrasion property at the distal end of the lip part which comes into contact with glass. This chlorine treatment comprises dipping at least the lip part of a wiper blade rubber in a chlorine-based solvent to harden the surface. When a wiper blade rubber treated with chlorine is operated in the water-wetted state on a glass surface subjected to a water-repellent treatment, chattering is generated. Furthermore, after the wiper is operated 100,000 times, a large number of streaks remain in the sensuous evaluation of the wiping property.
In order to ensure good visual field from a motor car or the like, the glass is sometimes subjected to a water-repellent treatment. According to the studies by the present inventors, this treatment has been confirmed to cause a problem in that the glass subjected to a water-repellent treatment repels water in a ball form and therefore, residual streaks and the like are not easily generated, however, since a water film is difficult to form, the glass and the rubber are liable to come into direct contact and even in the wet condition, the coefficient of friction particularly during the low-speed operation increases to be comparable with the coefficient of static friction in the dry condition and in turn, the coefficient of static friction in the wet condition becomes excessively large in comparison with the case of clean glass, as a result, the velocity dependence of the friction coefficient increases, so that a chattering (noise) is readily generated.
Even on a glass surface not subjected to a water-repellent treatment, when wax or the like is applied, chattering is sometimes readily generated because a water film is difficult to form. Also, the wiper blade rubber generates remaining streaks or uneven wiping, due to abrasion on use for a long period of time or due to mesh-geared sand, which inhibits the visual field.
Furthermore, with a long-term use, even a glass subjected to a water-repellent treatment undergoes partial loss of the water-repellent treatment and the glass substrate is exposed. Accordingly, the wiper blade rubber must have a good wiping performance and high noise-preventing effect for both a glass subjected to a water-repellent treatment and a clean glass.
By taking account of these problems, the object of the present invention is to provide a wiper blade rubber capable of exhibiting good wiping performance and high noise-preventing effect for both a glass subjected to a water-repellent treatment and a clean glass.
As a result of extensive investigations to achieve the above-described object, it has been found that this object can be attained by providing the following and the present invention has been accomplished based on this finding.
(1) A coating agent for wiper blade rubbers, comprising a particulate solid lubricant and a binder for sticking the solid lubricant to a wiper blade rubber, wherein the binder has a 0.5% modulus (substitute for an elastic modulus) of about 1 MPa or more and an elongation to break of about 1% or more after drying or curing.
(2) The coating agent for wiper blade rubbers as described in (1), wherein the volume ratio of the solid lubricant to the binder is from about 0.25 to about 1.0.
(3) The coating agent for wiper blade rubbers as described in (1), wherein the volume ratio of the solid lubricant to the binder is from about 0.4 to about 0.7.
(4) The coating agent for wiper blade rubbers as described in (1) to (3), wherein the solid lubricant is graphite particles.
(5) The coating agent for wiper blade rubbers as described In (1) to (4), wherein the binder is selected from the group consisting of urethane resins, polyamideimides resin and epoxy resins.
(6) The coating agent for wiper blade rubbers as described in (1) to (5), wherein the binder has a 0.5% modulus of about 4 MPa or more and an elongation to break of about 2% or more after drying or curing
(7) A wiper blade rubber having a coating film on both surfaces of a lip part thereof, the coating film comprising a particulate solid lubricant and a binder and the binder having a 0.5% modulus of about 1 MPa or more and an elongation to break of about 1% or more.
(8) The wiper blade rubber as described in (7), which is produced by a method comprising applying a coating agent on both surfaces of the lip part of a tandem-shaped wiper blade rubber, drying or curing the coating agent and cutting the distal end of the lip part to form coating films terminating on the lateral surface of the lip part.
(9) The wiper blade rubber as described in (7) and (8), wherein the coating film has a thickness of about 2 to about 10 xcexcm.
(10) The wiper blade rubber as described in (7) to (9), wherein when the terminal voltage of a motor for driving the wiper blade rubber is 7 V, the coefficient of static friction with a glass subjected to a water-repellent treatment is about 0.65 or less.
(11) The wiper blade rubber as described in (7) to (10), wherein the volume ratio of the solid lubricant to the binder is from about 0.25 to about 1.0.
(12) The wiper blade rubber as described in (7) to (10), wherein the volume ratio of the solid lubricant to the binder is from about 0.4 to about 0.7.
(13) The wiper blade rubber as described in (7) to (12), wherein the solid lubricant comprises graphite particles.
(14) The wiper blade rubber as described in (7) to (13), wherein the binder is selected from the group consisting of urethane resins, polyamideimide resins and epoxy resins.
(15) The wiper blade rubber as described in (7) to (14), wherein the binder has a 0.5% modulus of about 4 MPa or more and an elongation to break of about 2% or more after drying or curing.
(16) A method for producing a wiper blade rubber, comprising applying a coating agent on both surfaces of the lip part of a tandem-shaped wiper blade rubber, drying or curing the coating agent and cutting the distal end of the lip part to form coating films terminating on the lateral surface of the lip part, wherein the coating agent comprises a particulate solid lubricant and a binder and the binder has a 0.5% modulus of about 1 MPa or more and an elongation to break of about 1% or more after drying or curing.
(17) The method as described in (16), wherein the step of drying or curing the coating agent is a step of heat-treating the coating agent under conditions not more severe than about 120xc2x0 C. and about 30 minutes.
FIG. 1 is a cross-sectional view of a wire blade rubber having a tandem-shaped coating film used in the Mode for Carrying out the Invention and in the Examples.
FIG. 2 is a graph showing the relationship between the modulus at the elongation of 0.5% and the coefficient of static friction of various binders.
FIG. 3 is a graph showing the relationship between the transfer speed and the coefficient of friction on a water-repellent glass, of wiper blade rubbers of Example 1 and Comparative Example 1.
FIG. 4 is a graph showing the relationship between the transfer speed and the coefficient of friction on a glass not subjected to a water-repellent treatment, of wiper blade rubbers of Example 1 and Comparative Example 1.
FIG. 5 is a graph showing the relationship between the number of wiping operations and the sensory evaluation point on a clean glass not subjected to a water-repellent treatment.
FIG. 6 is a graph showing the abraded area (xcexcm2) is when a clean glass not subjected to a water-repellent treatment is wiped 100,000 times in Example 1 and Comparative Example 1.
FIG. 7 is a view showing the standard for the point number in the sensuous evaluation of wiping of FIG. 5.
A wiper blade rubber capable of exhibiting good wiping performance and high noise-preventing effect for a clean glass is known, which is designed by taking account of the balance among vibration absorption, low-temperature property, heat resistance, abrasion resistance, ozone resistance and the like. Such a wiper blade rubber is constructed, for example, by natural rubber, chloroprane, a blend of natural rubber and chloroprane, ethylene propylene rubber, silicone rubber, and so on In the present invention, any of these known wiper blade rubbers and the improved wiper blade rubbers can be used as a wiper blade rubber body. In the present invention, the friction is reduced by a surface modification method of coating the wiper blade rubber so as to prevent the wiping failure and the generation of noise on a water-repellent glass and improve wiping performance and noise preventing effect on a clean glass, so that a vibration absorption, low temperature property, heat resistance, ozone resistance, and the like, attributable to the characteristic features of the wiper blade rubber body can be maintained.
According to the present invention, a coating agent containing a particulate solid lubricant and a binder is coated on both surfaces of the lip part of a wiper blade rubber and then dried and/or cured to reduce the friction of the wiper blade rubber. The reduction in the coefficient of friction with a glass is mainly affected by the kind of the particulate solid lubricant, the kind of the binder and the blending ratio therebetween. The preferred solid lubricant is, but is not limited to, graphite. Particularly, scaly graphite is preferred because of its smaller coefficient of friction. In addition, polytetrafluoroethylene (emulsion polymerized particles are more preferred than suspension polymerized particles) and molybdenum disulfide may be used. Although particle size of the solid lubricant has a small effect, the particle size is set to be smaller than the thickness of the coating because the coefficient of friction is liable to be smaller as the particle size is smaller and also, the particles may drop in higher probability as the particle size is larger. In general, the thickness of the coating film is preferably from 2 to 10 xcexcm and therefore, the particle size of the solid lubricant is preferably smaller than the thickness of the coating. If the particle size of the particulate solid lubricant exceeds 10 xcexcm, the coating surface may be roughened to cause wiping failure on a clean glass.
The binder of the coating agent must have a 0.5% modulus of 1 MPa or more and an elongation to break of 1% or more after the drying or curing. Since the coating can be regarded as the lip of a wiper and the coefficient of friction during the abrasive operation is in inverse proportion to the elastic modulus, the 0.5% modulus (an elastic modulus) must be 1 MPa or more for obtaining a desired low coefficient of friction. If the elastic modulus is less than 1 MPa, the wiper blade rubber cannot have a sufficiently low coefficient of friction. The 0.5% modulus is preferably 4 MPa or more. However, it the elongation to break is less than 1%, the coating may be cracked and stripped upon cutting the distal end of the lip part after coating and drying or curing the coating agent or upon use. Therefore, the elongation to break must be 1% or more. The elongation to break is preferably 2% or more.
The resin capable of satisfying these properties as the binder is, but not particularly limited to, preferably a urethane resin, a polyamideimide resin or an epoxy resin.
The blending ratio of the solid lubricant to the binder (hereinafter referred to as a xe2x80x9cP/B ratioxe2x80x9d) is, in terms of a volume ratio, preferably from 0.25 to 1.0, more preferably from 0.4 to 0.7. If the amount of the solid lubricant is excessively large, desorption of particles readily occurs, whereas if the amount of the solid lubricant is small, the coefficient of friction is not sufficiently decreased and chattering (noise) is easily generated.
The thickness of the coating film is preferably from 2 to 10 xcexcm. If the thickness is less than 2 xcexcm, the obtained wiper blade rubber is disadvantageously large in the coefficient of friction with glass, whereas if it exceeds 10 xcexcm, the wiping failure occurs.
If desired, an appropriate solvent may be used The coating agent of the present invention contains a particulate binder and a particulate solid lubricant and usually, the solid contents comprising these binder and solid lubricant are dissolved in a solvent before use. The amount of the solvent used, based on the solid contents, varies depending on the use method of the prepared coating agent and cannot be specifically limited but the solvent is usually used in an amount of 150 to 1,200 parts by mass per 100 parts by mass of the solid portion.
The wiper blade rubber can be produced by a method comprising applying a coating agent on both surfaces of the lip part of a wiper blade rubber, drying or curing this coating agent and cutting the distal end of the lip part to form a coating film terminating on the lateral surface of the lip part.
The wiper blade rubber before the cutting preferably has a tandem shape. By having this shape, clear cutting of the distal end of the lip part is facilitated and a wiper blade rubber having a lip part attached with a coating film can be produced with good profitability.
The heat-treatment of drying or curing this coating agent is preferably performed under conditions not more severe than 120xc2x0 C. and 30 minutes. If the heat-treatment conditions are more severe than this, although it may vary depending on the construction material of the wiper blade rubber body, the wiper blade rubber body may be deteriorated to reduce the capability of wiping a clean glass or of preventing noises.
FIG. 1 is a view showing an example of coating the lip part of a wiper blade using this coating agent. As shown in FIG. 1, a coating agent 3 is coated, by spraying, on both surfaces of the lip part 2 of a wiper blade rubber 1 and then dried or cured to form a coating film. The wiper blade rubber is cut at the center of the lip part 2 to prepare wiper blade rubbers having coating films on the lip part. The numeral 4 shows the cutting face.